New asymmetrical ligands (H 2 L) have been synthesized to provide both a bridging and a terminal phenolate to a pair of iron ions in order to mimic the binding of a single terminal tyrosinate at the diiron center of the purple acid phosphatases. H 2 L1 is 2-[(bis(2-pyridylmethyl)amino)methyl]-6-[((2-pyridylmethyl)(2-phenol)amino)methyl]-4-methylphenol and H 2 L′1 and H 2 L2 are obtained by replacing the 2-phenol group by the 5-nitro-2-phenol and the 6-methyl-2-phenol residues, respectively. A series of mixed valence diiron complexes [Fe II Fe III L(X) 2 ](Y) have been obtained where (X) 2 is the dianion of m-phenylenedipropionate or (H 2 PO 4 ) 2 and Y )Diferric complexes have been obtained also either by direct synthesis or by iodine oxidation of the mixed valence precursor (L ) L1, 3a (X) 2 ) mpdp, Y ) BPh 4 , 3d: (X) 2 ) (H 2 PO 4 ) 2 , Y ) PF 6 ; L ) L2, 4d: (X) 2 ) (H 2 PO 4 ) 2 , Y ) PF 6 . Complex 1a [Fe II Fe III L(mpdp)](BPh 4 ) has been characterized by X-ray diffraction techniques. 1a crystallizes in the monoclinic space group P21/a with the following unit cell parameters: a ) 22.038 (9) Å, b ) 16.195 (8) Å, c ) 16.536 (7) Å, β ) 97.26 (1)°, Z ) 4. The significant differences in the Fe-O bond lengths indicate that the metal centers are ordered. The complexes have been studied by electronic spectral, resonance Raman, magnetic susceptibility, Mo ¨ssbauer, NMR, and electrochemical techniques. Mo ¨ssbauer and NMR spectroscopies concur to probe that the valences of the mixed valence compounds are trapped in solution as well as in the solid state at room temperature. The electronic spectrum of the mixed-valence compounds are dominated by a charge transfer transition in the 400-600 nm domain which moves to the 550-660 nm range upon oxidation to the diferric state. In addition they exhibit a weak and broad intervalence transition close to 1100 nm. Electrochemical studies show that the systems exist in the three redox states Fe